This invention relates to an engine test kit for auxiliary power units of the type commonly used on tracked military vehicles. Auxiliary Power Units (APUs) are generally small diesel engines in the 2 to 20 horsepower range and they are equipped with a D.C. starter-generator to charge the vehicle's batteries and operate the electrical system. APUs are also equipped with a hydraulic pump capable of operating the vehicle's hydraulic system.
The vehicle electrical and hydraulic systems do not require a significant portion of the main engine's power output; typically less than 5%, so normally the vehicle electrical and hydraulic systems are powered by the main engine. When the vehicle is stationary, most of the main engine's power is wasted. During these stationary periods, it is much more fuel efficient to operate the electrical and hydraulic systems with the smaller and more efficient APU than with the main engines. The APU can operate both the electrical and hydraulic systems to keep the vehicle in readiness without the need of operating the main engine. This significantly reduces the amount of noise emitted when the vehicle is in a quiet waiting state and also minimizes fuel consumption and main engine wear. Only when the vehicle is required to move is it necessary to operate the main engine.
On typical military vehicles such as the M88A1 Tracked Recovery vehicle and the M992 Tracked Ammunition Carrier, the APU is is located within an armored portion of the vehicle in a relatively inaccessible location. Even rudimentary testing and maintenance requires complete removal of the APU from the vehicle. The current practice for maintaining and repairing the APU requires removal of the APU from the vehicle, and visually inspecting the APU for sign of a problem. If an obvious problem is found from the inspections, or if a likely problem is suggested from an operational failure, that part is repaired or replaced and the APU reinstalled in the vehicle. Not infrequently, the repaired APU fails to function properly when replaced in the vehicle necessitating reremoval and repair.
A common problem with APUs has been faulty fuel injector pumps. This invention allows such operating problems to be diagnosed without disassembly of the APU while the APU is out of the vehicle. Repair of the fuel injector pumps is usually performed with an inexpensive fuel injector repair kit. In the past, testing the repairs effectiveness required placing the APU back in the vehicle and trying to operate the APU. The repair process often required up to five removal, repair, replacement and test cycles of the APU before the APU operated properly. Using my invention, the APU can be repaired and one person can perform the testing necessary to check out the APU. This saves personnel time since testing the APU in a vehicle requires one person to operate the controls while a second person monitors gauges attached to the APU. This was cumbersome and presents a safety problem because the person monitoring the APU had to work near an operating engine in a cramped engine compartment.
The prior procedure required use of the vehicle to test the APU and determine if the repair was successful. This procedure created an additional burden in that the vehicle must be kept out of service while the repair is being performed.
The test kit of my invention eliminates the need to reinstall the APU in the vehicle merely to perform diagnostic testing on the APU or to verify the repair. The invention consists of a portable test kit useful to test and repair an APU which is held securely on a test stand. One test stand can be configured to accept a variety of APUs by having multiple attachment points or by having reconfigureable attaching brackets and the required electrical, fuel and hydraulic connections to provide the necessary components to operate and test the APU. Switches and gauges on the test kit operate and monitor the APU so that most if not all trouble shooting functions can be performed at the test stand.
The test kit of the present invention is designed to be small, light weight, and easily moveable to assist in the removal and installation process. The mobility of the test kit allows the operator to bring the test stand to the vehicle, remove the APU, and move the test kit and APU to a convenient location for making the repair. This greatly assists the diagnoses and repair process because the size and weight of tracked military vehicles makes moving them inside difficult. Using this invention, the vehicle can be put in a relatively open area, the APU removed, fixed to the test stand and the APU brought to a more convenient location for diagnoses and repair. This allows even small repair facilities to handle repairs of the APU. If necessary, the vehicle can operate without the APU or with a replacement APU since the vehicle is not necessary for testing.